You probably already have the census info, but I'll list it here which may help others to connect:

1900 Clearfield county PA
Stinkavits
Simon 41 from Russ/Poland
Mary 38 Russ/Pol
Lida 12 Russ/Pol
Alexander 9 Russ/Pol
?Franklin 8 PA
?Peater 5 PA
Frances 2months old (born abt April 1900)
a boarder is also listed

1910 Clearfield county PA
Stenkavech
Simon 48 LT arr 1880
Mary 48 LT arr 1891
Alexander 19 arr 1891
Frank 17 PA
Peter 14 PA
Frances 12 PA
son in law Joseph Yo??? 21
daugher Lottie " 22
grandson Joseph " 1 month

1920 Clearfield county PA
Stemkovich
Mary 56 LT
Eleck 27
Frances 19

they are living next to Joseph and Lottie

WW2 draft info:

Alexander Stankavich b. 3/28/1891 Lithuania (no town given)
living at Hanover twp, Luzerne county PA
next of kin Mary Stankavich 735 Westlong Ave DuBois PA

Frank Stankavich b. 3/19/1893 DuBois PA
living at 2707 Penny Erie PA
contact person VJ Ross at 2705 Penny Erie PA.

From the draft info, it looks like Alexander and Frank were not married, at least as of 1942.

And from the census info, Simon must of died as of the 1920 census.

I could not find them on either Ellis Island (where records start in 1892) or on the Castle Garden data base. But the old manifests don't give much information either. You may want to check for any naturalization records with the state of PA, and to get Mary's maiden name, send for a social security application on her children (or herself) should provide some information.